1. Field of the Invention
The present invention generally relates to a picture reading apparatus, and more particularly to a picture reading apparatus with flaring light elimination capability, which is applicable to a picture reading part of a facsimile machine, an image scanner or the like.
2. Discussion of the Background
Japanese Laid-Open Patent Application No. 1-265660 discloses a conventional picture reading apparatus in which a focusing lens array is used, as shown in FIG. 1. In FIG. 1, the picture reading apparatus includes a non-reduction type image pickup element 21, slit plates 22, a fluorescent lamp 23, a light converging lens 24, a focusing lens array 25, and a contact glass 28. Light that is emitted by the fluorescent lamp 23 is converged by the light converging lens 24 and this converging light is irradiated to a document 26 through the contact glass 28. The document 26 is scanned in a main scanning direction, which is perpendicular to the sheet of FIG. 1, by the light from the fluorescent lamp 23. Because the document is transported in a direction indicated by an arrow A in FIG. 1, the scanning of the light from the fluorescent lamp 24 is also made in a sub scanning direction which is perpendicular to the main scanning direction. An irradiation width or length 27 of the light from the fluorescent lamp 23 in the sub scanning direction, where the light is irradiated to the document 26, is limited by the slit plates 22 the edge portions of which form a slit at a portion between the light converging lens 24 and the contact glass 28. This irradiation width is thus limited to less than 30 mm in the sub scanning direction, preferably to less than 2 mm.
On the other hand, light that is reflected from the document 26 is focused by the focusing lens array 25 on the non-reduction type image pickup element 21, and this image pickup element 21 supplies a picture signal indicative of a picture from the document 26. However, there appears irregular reflection light irregularly reflected by a document surface, where the scanning is not made by the emitted light from the light source, or by a portion of the contact glass 28, which irregular reflection light may enter directly the focusing lens array 25, thereby deteriorating the quality of a picture being reproduced from the picture signal supplied by the image pickup element 21. The conventional picture reading apparatus has no effective means for preventing such reflected light from entering directly the focusing lens array and from being led to the image pickup element. Therefore, there is a problem in that the conventional picture reading apparatus does not show enough image focusing performance, because it has no means for preventing undesired light, other than the converged light from the light source effective in supplying a picture signal, from entering directly inside of the focusing lens array.
FIG. 2 shows another example of the conventional picture reading apparatus to which a roof mirror lens array (RMLA) is applied. This picture reading apparatus as shown in FIG. 2 includes an optical path separation mirror (SM) 31, a lens array (LA) 32, a roof mirror array (RMA) 33, a restricting plate (not shown) provided between the LA 32 and the RMA 33, and a housing (not shown) for holding the above mentioned component parts and shielding the inside of the apparatus from external light. Light from an object 34 to be scanned is reflected by the SM 31 and this reflected light passes through the LA 32 and is irradiated to the RMA 33. The lens array 32 has a plurality of lenses arranged consecutively at equal intervals in the main scanning direction, as indicated by an arror Y in FIG. 2, and each lens of the lens array 32 converges the reflected light from the separation mirror 31 into a converged light which is led to the RMA 33. The separation mirror 31 serves to separate an optical path of light, being led from the object 34 to the lens array 32, from an optical path of the converging light from the lens array toward the SM 31. The roof mirror array 33 which has a plurality of roof-like reflection surfaces arranged consecutively at equal intervals in the main scanning direction, as indicated by the arrow Y in FIG. 2. The converging light, being led from each lens of the lens array 32 to the SM 31, is again reflected by each roof-like reflection surface of the roof mirror array 33, and this reflected light is focused as an image 35 on a position symmetrical to the position of the object 34 with respect to the plane of the picture reading apparatus.
The image 35 is an erect image with respect to the object 34 both in the main scanning direction Y and in the sub scanning direction as indicated by an arrow X in FIG. 2. In particular, this image is a non-reduction erect image having a scale factor equal to 1 in the sub scanning direction X. Therefore, the necessary scanning width is covered by overlapping an image formed by means of a lens of the LA and a roof mirror of the RMA in the sub scanning direction X. The lenses of the LA, the roof-like reflection surfaces of the RMA and the restricting plates must be respectively arranged at equal intervals therebetween, and each lens of the lens array 32 must show essentially the same light quantity distribution. For this reason, the distribution of light quantity of each lens in the LA 32 is predetermined to be uniform in the main scanning direction Y.
However, in the case of the conventional picture reading apparatus as shown in FIG. 2, the emitted light from the light source passes through a transparent portion of the separation mirror, and such light is irregularly reflected or scattered in the RMLA optical system, resulting in a flaring light which particularly lowers the image focusing performance of the picture reading apparatus. In addition, the conventional picture reading apparatus described above employ a slit which is arranged between the light source and the document. However, the use of a slit by the picture reading apparatus requires an increase in the total number of parts needed, and also requires additional time to perform manufacturing steps of positioning and adjustment of a slit in the picture reading apparatus.